Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup optical system to be used in an image pickup apparatus, such as a digital camera, a video camera, a broadcasting camera, a monitoring camera, or a silver-halide film camera.
Description of the Related Art
In recent years, as image pickup optical systems to be used in image pickup apparatus, such zoom lenses have been demanded that are small and light-weight as a whole and have a short total lens length and a high zoom ratio. As zoom lenses satisfying those demands, there have been known positive lead type zoom lenses in which a lens unit having a positive refractive power is arranged closest to an object side.
In Japanese Patent Application Laid-Open No. 2012-47814, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a sixth lens unit having positive, negative, positive, positive, negative, and positive refractive powers, and is configured to change an interval between adjacent lens units during zooming.
It is relatively easy to obtain a positive lead type zoom lens that is small as a whole and has a high zoom ratio. In positive lead type zoom lenses, an axial ray passes through a first lens unit at a position away from an optical axis in many cases. Thus, in the positive lead type zoom lenses, an effective diameter of the first lens unit tends to be increased, leading to the large first lens unit. Further, when a zoom ratio is increased while a focal length at a telephoto end is long, various aberrations such as a spherical aberration, coma, and a chromatic aberration are generated in the first lens unit by a large amount on the telephoto side of a zoom range.
In the positive lead type zoom lenses, the lens structure of the first lens unit greatly affects the optical characteristics of the zoom lens, and the size of the first lens unit greatly affects the entire size and weight of the zoom lens. Accordingly, in order to obtain a positive lead type zoom lens that is small and light-weight as a whole and has a high zoom ratio and high optical characteristics over an entire zoom range, it is important to appropriately determine the lens structure of a first lens unit in addition to the number of lens units and refractive powers of the respective lens units.